To improve energy efficiency in lighting apparatuses, research and development are being pursued to obtain light sources that take the place of incandescent lamps and fluorescent lights. Recently, high luminance light emitting diodes (LEDs) and the like are regarded as one of the most promising candidates, and their application products are actually being manufactured on a commercial basis. Reflecting this trend, commercialization of lightings with use of organic electroluminescence elements (hereinafter referred to as organic EL elements) are coming close to fruition.
The LED lightings need to diffuse light by some method since the light emitting elements emit light as point light. As compared with this, a panel itself emits light in the organic EL lightings, so that wide and uniform light can advantageously be obtained. Moreover, since the panel is extremely thin, the panel can be pasted on walls, ceilings and the like, so that the wall surfaces of rooms themselves can be used as a lighting. The panel can also be pasted on curved surfaces by using a plastic substrate.
The organic EL elements gradually deteriorate and their luminance is degraded under the influence by operation, oxygen and/or humidity. In recent years, in order to extend the lives of the organic EL elements, development of luminescent materials with sufficient chemical stability, and innovation of techniques in sealing, bonding and the like with respect to element structures have been advanced. As a result, life characteristics of the organic EL elements have considerably been improved. The extension of life is also pursued by suppressing a driving current of the organic EL elements.
For example, Patent Literature 1 discloses a display device in which, among a plurality of light emitting layers different in luminescent color from each other, a light emitting layer low in luminous efficiency is provided in plural inside a unit display range, so as to increase the area of the light emitting layers in the unit display region for the purpose of suppressing the driving current while gaining white balance.